Abstract
Wet flue gas desulfurization (WFGD) wastewater treatment is a key problem in coal-fired plants. Traditional chemical precipitation methods cannot reach zero-liquid discharge (ZLD). In this paper, a new technology using the low-rank heat from flue gas to concentrate the wastewater for ZLD is proposed. A scrubber was built to verify the concentrating process, and the characteristics of the concentrated water were analyzed. The concentrated water was neutralized by adding Ca(OH)2 to raise the pH value. The wastewater can be concentrated 10~25 times to reduce the flow rate. The characteristics of the concentrated wastewater were studied by dosing lime. Then, liquid and solids were separated by filter pressing, the liquid was mainly composed of CaCl2, which accounts for 73.6%. The sludge is composed of CaSO4 and Mg(OH)2, depending on the lime consumption of the dosing process. Finally, the filter liquor after the filter press was mixed with ash to reach zero liquid discharge, and the sludge could be burnt after mixing with the coal or disposed by third-part vendor. This technology is demonstrated in one 600 MW unit and shows a high system reliability. The clean water is recycled by the WFGD wastewater during the evaporation. Binding on the environmental policies and large market demand of the WFGD wastewater, this technology shows a great application prospect in the future.
Highlights
The limestone–gypsum wet flue gas desulfurization (WFGD) uses limestone as an absorbent to capture SO2 in the flue gas, and produces gypsum as a byproduct [1,2,3,4,5,6,7]
By adding the sodium carbonate, organic sulfur and flocculating agent (PAM) to the WFGD wastewater, Ca2+, Mg2+ and the heavy metals are precipitated from the wastewater
The concentrated wastewater containing high chloride ion is mixed with the ash collected by the ESP to reach zero-liquid discharge [18,19,20,21]
Summary
The limestone–gypsum wet flue gas desulfurization (WFGD) uses limestone as an absorbent to capture SO2 in the flue gas, and produces gypsum as a byproduct [1,2,3,4,5,6,7]. Most salt irons including chloride ions remain in the filtered solution, which is directly discharged from the power plant [16,17]. This may cause secondary pollution to the surface water environment. As the concentration ratio of the RO membrane is very low, the method will cause large amount of steam [13,14] Another method for the wastewater treatment is direct drying process. The concentrated wastewater containing high chloride ion is mixed with the ash collected by the ESP to reach zero-liquid discharge [18,19,20,21]. There is no wastewater discharged from the power plant and actual achieve the wastewater’s zero emission
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